This invention relates to systems and methods for fuel control in vehicle engines and, in particular, to a system and method for adapting engine fuel control based on the volatility quality of the fuel.
A conventional vehicle having a fuel-injected internal combustion engine includes a system for controlling the amount of fuel injected into each cylinder of the engine during a combustion event. The amount of fuel is controlled to achieve an optimal air-fuel ratio in the cylinders and thereby reduce emissions of hydrocarbons (HC), carbon monoxide (CO) and nitrous oxides (NOx). A fuel such as gasoline, however, includes more than two hundred (200) different hydrocarbon elements with many different boiling points. As a result, different elements in the fuel vaporize at different rates within the engine. Many conventional systems fail to account for this difference in vaporization rates. As a result, conventional systems fail to obtain an optimal air-fuel ratio-particularly during cold starts when the systems must operate using an open-loop control strategy because typical air-fuel measurement indicators such as oxygen sensors are not yet functional.
In commonly assigned U.S. Pat. No. 6,067,965, the entire disclosure of which is incorporated herein by reference, a system is disclosed in which the different vaporization rates of fuel elements are taken into account in controlling fuel injection in the engine. Once a desired combustion fuel quantity is determined, the system derives a desired fuel injection quantity based on the desired combustion fuel quantity and a previous fuel injection quantity. The prior fuel injection quantity is parsed into a plurality of components each having a mass fraction value and a vaporization constant based partly on engine temperature. An estimate of the mass of vapor produced is then obtained and is used to determine the desired fuel injection quantity. The disclosed system represents a significant improvement over conventional systems. The system does not, however, account for different fuel volatility characteristics. The volatility characteristics of gasoline provided to consumers varies widely depending upon a variety of factors such as geographic location and weather. For example, in the northern United States, fuels having a relatively high volatility are required during winter months when air temperatures are relatively cold in order to enable sufficient fuel vaporization for cold engine starts. During summer months when air temperatures are relatively warm, however, fuels having a relatively low volatility are required to prevent vapor lock resulting from premature fuel vaporization in the fuel delivery system. Because variations in fuel result in variable volatility and vaporization rates, assumptions regarding fuel volatility made in the disclosed system of U.S. Pat. No. 6,067,965 may result in a non-optimal air-fuel ratio.
There is thus a need for a system and method for controlling the injection of a fuel into a cylinder of an internal combustion engine that will minimize and/or eliminate one or more of the above-identified deficiencies.
The present invention provides a system and method for controlling injection of a fuel into a cylinder of an internal combustion engine. The fuel may be represented as a plurality of liquid components having different boiling points. Each component may include a single element of the fuel or more than one element of the fuel. For example, a component may include those elements of the fuel having boiling points within a specified range. Each component has a mass fraction value associated therewith. The mass fraction value corresponds to an estimate of the mass of the component relative to the total mass of the fuel (i.e. of all the components and/or elements).
A method in accordance with the present invention includes the step of determining a combustion air-fuel ratio for a previous combustion event in one of a first cylinder (i.e., the cylinder into which the fuel will be injected) and a second cylinder of the engine. The combustion air-fuel ratio may be determined using an exhaust oxygen sensor, for example. The method also includes the step of measuring a temperature of the engine. The method further includes the step of adjusting a plurality of the mass fraction values responsive to the combustion air-fuel ratio and the temperature to obtain a modified set of mass fraction values for the fuel. Finally, the method includes the step of providing the fuel to the first cylinder responsive to the modified set of mass fraction values.
A system in accordance with the present invention includes an oxygen sensor that generates an air-fuel ratio signal indicative of a combustion air-fuel ratio for a previous combustion event in one of a first cylinder and a second cylinder of the engine. The system further includes a temperature sensor that generates a temperature signal indicative of a temperature of the engine and a fuel injector. Finally, the system includes an electronic control unit (ECU) configured to adjust a plurality of the mass fraction values responsive to the combustion air-fuel ratio and the temperature to obtain a modified set of mass fraction values for the fuel. The ECU is further configured to provide the fuel to the first cylinder responsive to the modified set of mass fraction values.
The present invention represents an improvement as compared to conventional systems and method for controlling delivery of fuel to the engine cylinders. The inventive system and method are able to account for changes in fuel volatility characteristics by monitoring changing engine conditions and adjusting values representative of the fuel. As a result, the inventive system and method are more likely, as compared to conventional systems and methods, to maintain an optimal air-fuel ratio in the engine thereby reducing emissions and improving engine performance.
These and other advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.